Polyethylene blend compositions

ABSTRACT

Disclosed herein are various processes, including a process for producing a film, comprising (including) forming a film from a blended polyolefin composition at a line speed of at least 170 feet per minute, wherein the blended polyolefin composition comprises: (a) a bimodal polyethylene component that includes a high molecular weight polyethylene component having a high average molecular weight (MW HMW ) and a low molecular weight polyethylene component having a low average molecular weight (MW LMW ), wherein the ratio of the high average molecular weight to the low average molecular weight (MW HMW :MW LMW ) is 20 or more wherein the high and low molecular weight polyethylene components of the bimodal polyethylene component are formed in a single reactor; and (b) a unimodal polyethylene component that occupies more than 15 wt % of the composition.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Divisional application under 37 C.F.R. 1.53(b) ofand claims priority under 35 U.S.C. §120 to U.S. patent application Ser.No. 11/053,751 filed on Feb. 7, 2005 now U.S. Pat. No. 7,312,279 . Thisapplication is hereby incorporated by reference in its entirety.

BACKGROUND

1. Field of Invention

Embodiments of the present invention generally relate to processes forproducing films from compositions containing blends of polyethylenes,particularly processes for producing films from compositions containingblends of bimodal polyethylene and unimodal polyethylene, and film resincompositions.

2. Description of Related Art

Polyethylene compositions have been used to make films, includingbimodal polyethylene compositions. Bimodal polyethylene compositionshave numerous advantages over unimodal polyethylene compositions, andhave solved various problems in the art. High molecular weight bimodalhigh density polyethylene compositions have been used to make film aswell as pipes. Unlike pipe resins, a film resin has to satisfy severalcritical processing attributes: bubble stability, draw-down capability,and film quality. Many good bimodal pipe resins do not necessarily serveas good film resins, which require the above mentioned film processingattributes. In some cases, certain bimodal pipe resins exhibit poorbubble stability and poor film quality, when they are film extruded,with undesirable film texture where many hazy lines are dispersed allover the film surface, and therefore are unsatisfactory for filmapplications.

The undesirable film texture of hazy lines dispersed on the film surfaceis believed to stem from inhomogeneous molten polymer. When the bimodalpolyethylene, which consists of high molecular weight component and lowmolecular weight component, is extruded from an annular die and expandedto form a blown bubble, crystallization takes place near the frost line.If the two components of the bimodal polyethylene are not wellhomogenized in a molten state, either due to their huge disparity inmolecular weight or in viscosity, the respective component crystallizesseparately forming discrete phases in a solid state. This results inpoor film texture with hazy lines dispersed all over the film surface.

The homogeneity of bimodal polyethylene is believed to be dependent onthe degree of spread, which describes the bimodality of the bimodalpolyethylene, i.e., the relative distance between the two molecularweight peaks of component polymers, which can be seen from a sizeexclusion chromatography. It appears to be an optimum range of spreadthat prevents a blown film of bimodal polyethylene from being resultedin poor film texture.

Often, bimodal polyethylenes of poor film texture are accompanied withpoor bubble stability. The inhomogeneity of the molten polymer leads topoor melt strength, which results in a limited capability of filmblowability, i.e., poor bubble stability and, poor draw-down capability.

An ongoing need exists for further understanding on the film blowabilityof polyethylene resin, particularly for bimodal polyethylenecompositions used to make films. This invention discusses polyethylenecompositions that comprise of bimodal polyethylene having a wider spreadand unimodal polyethylene.

Earlier patents and published applications describe various aspects ofpolyethylene compositions that contain mixtures of different types ofpolyethylenes, including Sakurai et al., U.S. Pat. No. 4,336,352 whichinvolves blends of different ethylene polymers; Whaley, U.S. Pat. No.6,359,072, which involves films formed from blends of polyethyleneresins; Debras et al., U.S. Pat. No. 6,566,450, relates to multimodalpolyethylenes; Laurent, U.S. Pat. No. 6,579,922 involves pipe resinblends that include bimodal polyethylene; McDaniel et al., U.S. Pat. No.6,525,148, relates to catalyst systems for making polyethylenes; Cluttonet al., U.S. Pat. No. 6,489,427, relates to polymer compositions;McDaniel et al., U.S. Pat. No. 6,388,017, relates to various polymercompositions; de Lange et al., U.S. Pat. No. 6,545,093, relates tobimodal polyethylene blends; Nummila-Parkarinen et al., U.S. Pat. No.6,562,905, relates to high density polyethylene compositions; Promel,U.S. Pat. No. 6,344,522, relates to ethylene polymer compositions;Jacobsen et al., U.S. Pat. No. 6,506,866 relates to ethylene copolymercompositions; Vandun et al., PCT Application WO 03/016396, relates tobimodal polyethylene compositions; Mattioli et al., PCT Application WO02/102891 relates to ethylene polymer compositions; Ahistrand, EP 1 146078, relates to polymer compositions for pipes; and Laurent, EP 1 041113, relates to polyolefins.

Also, patents that refer to films and/or polyethylene compositions, aswell as methods for making polyethylene, include the following: U.S.Pat. Nos. 4,336,352; 5,091,228; 5,110,685; 5,208,309; 5,274,056;5,635,262; 5,338,589; 5,344,884; 5,378,764; 5,494,965; 5,739,225;5,795,941; 6,090,893; 6,340,730; 6,359,072; 6,388,017; 6,388,115;6,403,717; 6,420,580; 6,441,096; 6,476,166; 6,534,604; 6,562,905;6,605,675; 6,608,149; and WO 97/47682 and WO 94/22948. Other patents andpublications are listed on the cover page of the patent.

SUMMARY

Disclosed herein are various processes, including processes forproducing a film, comprising (including) forming a film from a blendedpolyolefin composition at a line speed of at least 170 feet per minute,wherein the blended polyolefin composition comprises: (a) a bimodalpolyethylene component that includes a high molecular weightpolyethylene component having a high average molecular weight (MW_(HMW))and a low molecular weight polyethylene component having a low averagemolecular weight (MW_(LMW)), wherein the ratio of the high averagemolecular weight to the low average molecular weight (MW_(HMW):MW_(LMW))is 20 or more wherein the high and low molecular weight polyethylenecomponents of the bimodal polyethylene component are formed in a singlereactor; and (b) a unimodal polyethylene component that occupies morethan 15 wt % of the composition.

Specific embodiments of these and other processes are disclosed below.

DETAILED DESCRIPTION

Definitions and Properties

Various terms as used herein are defined below. To the extent a term isused in a claim is not defined below, or elsewhere herein, it should begiven the broadest definition that persons in the pertinent art havegiven that term as reflected in printed publications and issued patents.

For purposes of convenience, various specific test procedures areidentified for determining properties such as PDI, FI and MFR. However,when a person of ordinary skill reads this patent and wishes todetermine whether a composition or polymer has a particular propertyidentified in a claim, then any published or well-recognized method ortest procedure can be followed to determine that property, although thespecifically identified procedure is preferred. Each claim should beconstrued to cover the results of any of such procedures, even to theextent different procedures may yield different results or measurements.Thus, a person of ordinary skill in the art is to expect experimentalvariations in measured properties that are reflected in the claims. Allnumerical values can be considered to be “about” or “approximately” thestated value, in view of the nature of testing in general.

Density is a physical property of a composition, is determined inaccordance with ASTM-D-1505, and is expressed as grams per cubiccentimeter (or grams per milliliter).

Except to the extent the actual density is specified, the term “highdensity” means any density of 0.935 g/cc or above, preferably 0.945 g/ccor above, or more preferably 0.950 g/cc or above, and a preferable rangeof a high density composition is from 0.945 g/cc to 0.967 g/cc.

The term “polyethylene” means a polymer made of at least 50%ethylene-derived units, preferably at least 70% ethylene-derived units,more preferably at least 80% ethylene-derived units, or 90%ethylene-derived units, or 95% ethylene-derived units, or even 100%ethylene-derived units. The polyethylene can thus be a homopolymer or acopolymer, including a terpolymer, having other monomeric units. Apolyethylene described herein may, for example, include units derivedfrom a co-monomer that is preferably an α-olefin, e.g., propylene,1-butene, 1-pentene, 1-hexene, or 1-octene. Other embodiments mayinclude ethacrylate or methacrylate.

As used herein, the term “PDI” means polydispersity index, and means thesame thing as “MWD” (molecular weight distribution), which ischaracterized herein using Size-Exclusion Chromatography (SEC).

The term “multimodal polyethylene composition” as used herein, means acomposition that includes at least a bimodal polyethylene (or multimodalpolyethylene), but the meaning of the term also encompasses acomposition that is preferred herein, which is a blend of a bimodalpolyethylene and a unimodal polyethylene.

The term “bimodal,” when used herein to describe a polymer or polymercomposition, e.g., polyethylene, means “bimodal molecular weightdistribution,” which term is understood as having the broadestdefinition persons in the pertinent art have given that term asreflected in printed publications and issued patents. For example, asingle composition that includes polyolefins with at least oneidentifiable high molecular weight distribution and polyolefins with atleast one identifiable low molecular weight distribution is consideredto be a “bimodal” polyolefin, as that term is used herein. Preferably,other than having different molecular weights, the high molecular weightpolyolefin and the low molecular weight polyolefin are bothpolyethylenes but may have different levels of comonomer distribution. Amaterial with more than two different molecular weight distributions(sometimes referred to as a “multimodal” polymer) will be considered“bimodal” as that term is used herein.

The term “unimodal,” as used herein to describe a polymer or polymercomposition, means any polymer, e.g., polyethylene, that is not bimodalas defined above, e.g., one having a single molecular weightdistribution.

The term “dual catalyst system” includes a bimetallic catalyst as wellas a multiple-catalyst system, and includes any composition, mixture orsystem that includes at least two different catalyst compounds, eachhaving a different metal group. Preferably, each different catalystcompound resides on a single support particle, so that the dual orbimetallic catalyst is a supported dual or bimetallic catalyst. However,as used herein, the term bimetallic catalyst also broadly includes asystem or mixture in which one of the catalysts resides on onecollection of support particles, and another catalyst resides on anothercollection of support particles. Preferably, in that latter instance,the two supported catalysts are introduced to a single reactor, eithersimultaneously or sequentially, and polymerization is conducted in thepresence of the dual or bimetallic catalyst system, i.e., the twocollections of supported catalysts.

Also, the term “dual catalyst system” that includes a bimetalliccatalyst as well as a multiple-catalyst system, and includes anycomposition, mixture or system that includes at least two differentcatalyst compounds, each having a different metal group, can be slurriedtogether with the supported MAO (methyl aluminoxane). The slurriedcatalysts, mixed either on line or off line, are introduced to a singlereactor, and polymerization is conducted.

The term “FI” means I₂₁, which is measured in accordance with ASTM-1238,Condition E, at 190 degrees C.

The term “MFR (I₂₁/I₂)” means the ratio of I₂₁ (also referred to as FI)to I₂, and both I₂₁ and I₂ are measured in accordance with ASTM-1238,Condition E, at 190 degrees C.

The “overall” number average, weight average, and z-average molecularweight are terms that refer to the molecular weight values for theentire composition, as opposed to that of any individual component.Overall molecular weight values referenced in the claims encompass anyvalue as determined by any published method, including those mentionedin the paragraph above; however, a preferred method is using an SECcurve.

The number average, weight average and z-average molecular weight(particularly the weight average molecular weight) of a particularpolyethylene component recited in the claims, e.g., the high molecularweight component and the low molecular weight component, can also bedetermined any published method, including those mentioned in theparagraphs above; however, a preferred method is using any publisheddeconvolution procedure, e.g., any published technique for elucidatingeach individual component polymer's molecular information in a bimodalpolymer. A particularly preferred technique is one that uses a Florydeconvolution, including but not limited to the Flory procedures setforth in U.S. Pat. No. 6,534,604 which is incorporated by reference inits entirety. Any program that incorporates the principles contained inthe following reference is useful: P. J. Flory, Principles of PolymerChemistry, Cornell University Press, New York 1953. Any computer programcapable of fitting an experimental molecular weight distribution withmultiple Flory or log-normal statistical distributions is useful. TheFlory distribution can be expressed as follows:

$Y = {{A_{o}\left( \frac{M}{M_{n}} \right)}^{2}{\mathbb{e}}^{(\frac{M}{M_{n}})}}$

In this equation, here Y is the weight fraction of polymer correspondingto the molecular species M, Mn is the number average molecular weight ofthe distribution, and A_(o) is the weight fraction of the sitegenerating the distribution. Y can be shown to be proportional to thedifferential molecular weight distribution (DMWD) which is the change inconcentration with the change in log-molecular weight. The SECchromatogram represents the DMWD. Any computer program that minimizesthe square of the difference between the experimental and calculateddistributions by varying the A_(o) and Mn for each Flory distribution ispreferred. Particularly preferred is any program that can handle up to 8Flory distributions. A commercially available program, called ExcelSolver, offered by Frontline Systems, Inc. at www.solver.com can be usedto perform the minimization. Using this program, special constraints canbe placed on the individual Flory distributions that allow one to fitchromatograms of experimental blends and bimodal distributions.

Bimodal distributions can be fit with two individual groups of fourconstrained Flory distributions, for a total of eight distributions. Oneconstrained group of four fits the low molecular weight component whilethe other group fits the high molecular weight component. Eachconstrained group is characterized by A_(o) and Mn of the lowestmolecular weight component in the group and the ratios A_(o)(n)/A_(o)(1)and Mn(n)/Mn(1) for each of the other three distributions (n=2,3,4).Although the total number of degrees of freedom is the same for theconstrained fit as for eight unconstrained Flory distributions, thepresence of the constraint is needed to more accurately determine thecontribution to the total chromatogram of the individual low molecularweight and high molecular weight components in a bimodal polymer. Oncethe fitting process is complete, the program will then calculate themolecular weight statistics and weight percents of the individual highand low molecular weight components. FIG. 1 depicts a deconvoluted curveof each individual component.

The term “split” is defined herein as the weight % of a high molecularweight component in a bimodal composition. Thus, it describes therelative amount of the higher molecular weight component against thelower molecular weight component in a bimodal polyethylene composition,including any of the polymer compositions described herein. The weight %of each component can polymer is also be represented by the area of eachmolecular weight distribution curve that is seen after deconvolution ofthe overall molecular weight distribution curve.

The term “spread” as used herein means the ratio of the weight averagemolecular weight of the high molecular weight polyethylene component,sometimes referred to as Mw_(HMW), to the weight average molecularweight of the low molecular weight polyethylene component, sometimesreferred to as Mw_(LMW). The “spread” can therefore be also expressed asthe ratio of Mw_(HMW):Mw_(LMW). Weight average molecular weight of eachcomponent can be obtained by deconvolution of an overall SEC curve,i.e., an SEC curve of an entire composition.

As used herein (e.g., in the claims), the term “maximum line speed”(“Maximum Line Speed” or MLS) is a measured property of a polymer, blendor other composition, and is defined as the maximum line speed as thatterm is used by persons skilled in the art of making film (discussedbelow), based on the particular extrusion equipment and conditions setforth in Example 1, below. In the art of making film, the maximum linespeed refers to a particular take-up speed at which the blown bubblestarts to show symptoms of “bubble instability,” a characteristicrecognized by persons skilled in the art of making polyethylene film.When a film is being formed during the blown film extrusion process,take-up speed is slowly increased for a given output rate (which can beset by a fixed screw rpm), a given melt extrusion temperature (which canbe set by the die temperature) and cooling air flow rate. As the take-upspeed is increased, the blown bubble becomes thinner and thinner. Ahigher take-up speed yields thinner film, which is typically moredesirable since less resin is needed to produce a given amount of filmgoods. However, take-up speed is limited by bubble instability, which isseen, for example, by up-and-down movement of frost line height, dancingaround or twisting of a blown bubble along the center axis, or theoscillation or wobbling of a blown bubble along its axis. Bubbleinstability can be made to disappear by reducing take-up speed. TheMaximum Line Speed is expressed herein in units of feet per minute(fpm), and it is understood herein that each Maximum Line Speed valueincludes plus or minus 10%, i.e., the recognition that experimental,equipment and/or operator error can cause a variance of plus or minus10% for a given composition.

SPECIFIC EMBODIMENTS

Various specific embodiments are described below, at least some of whichare also recited in the claims. In one embodiment, the compositiondescribed in the summary, or the composition described in the claims, orany of the compositions described herein, can have some of the followingcharacteristics

The polyethylene composition can in some cases be formed into a film,preferably an extruded film, but also blown film or other types offilms.

In at least certain embodiments, the overall spread is less than 95% ofthe bimodal polyethylene spread, while in other embodiments, the overallspread is 90% or less, or 85% or less, or 80% or less, or 75% or less ofthe bimodal polyethylene spread. The “overall spread” is defined hereinas the ratio of the weight average molecular weight of the highmolecular weight component of the composition (the blend) to the weightaverage molecular weight of the low molecular weight component of thecomposition, and a “bimodal polyethylene spread,” defined as the ratioof the weight average molecular weight of the high molecular weightcomponent of the bimodal polyethylene component to the weight averagemolecular weight of the low molecular weight component of the bimodalpolyethylene component. It is noted that the “bimodal polyethylenespread” is determined without the presence of any portion of theunimodal polyethylene component, e.g., before the bimodal component andthe unimodal component are blended.

Preferably, in the polyethylene composition described in the summary andelsewhere herein, the unimodal polyethylene component has a molecularweight distribution peak falling between two peaks of the bimodalpolyethylene.

The unimodal polyethylene component can in certain cases occupy morethan 30 wt % of the composition.

The bimodal polyethylene component can in certain cases occupy more than50 wt % of the composition.

The unimodal polyethylene component can in certain cases have a densityof 0.935 g/cc or more and a PDI of 8 or more.

The bimodal polyethylene component can in certain cases have a densityof 0.935 g/cc or more and a spread of 20 or more.

The bimodal polyethylene component can in certain cases have a densityof 0.935 g/cc or more and a PDI of 20 or more.

The PDI of the high molecular weight component of the bimodalpolyethylene can in certain cases be greater than 3.5.

The PDI of the low molecular weight component of the bimodalpolyethylene can in certain cases be 2.5 or more.

The average molecular weight of the composition can in certain cases be200,000 or more.

The ratio of high average molecular weight to the low average molecularweight can in certain cases be 10 or more.

The average molecular weight of the bimodal polyethylene component canin certain cases be 250,000 or more.

The FI (I₂₁) of the composition can in certain cases be from 5 to 15g/10 min.

The FI (I₂₁) of the bimodal polyethylene component can in certain casesbe from 5 to 15 g/10 min.

The MFR (I₂₁/I₂) of the composition can in certain cases be from 70 to250.

The MFR (I₂₁/I₂) of the bimodal polyethylene component can in certaincases be from 70 to 250.

The high molecular weight polyethylene component can in certain casesoccupy 40 wt % or more of the bimodal polyethylene component.

The high and low molecular weight polyethylene components of the bimodalpolyethylene component can in certain cases be formed in a singlereactor.

The high and low molecular weight polyethylene components of the bimodalpolyethylene component can in certain cases be formed in gas phasepolymerization.

The bimodal polyethylene component can in certain cases be made frompolymerization conducted in the presence of a multiple catalyst systemthat includes a metallocene based catalyst.

The bimodal polyethylene component can in certain cases be made frompolymerization conducted in the presence of a multiple catalyst systemthat includes a Zieglar-Natta based catalyst.

The high and low molecular weight polyethylene components of the bimodalpolyethylene component can in certain cases be formed frompolymerization conducted in the presence of a multiple catalyst systemthat includes bis(2-(trimethylphenylamido)ethyl)amine zirconiumdibenzyl.

The high and low molecular weight polyethylene components of the bimodalpolyethylene component can in certain cases be formed frompolymerization conducted in the presence of a multiple catalyst systemthat includes bis(2-(pentamethyl-phenylamido)ethyl)amine zirconiumdibenzyl.

The high and low molecular weight polyethylene components of the bimodalpolyethylene component can in certain cases be formed frompolymerization conducted in the presence of a multiple catalyst systemthat includes pentamethylcyclopentadienyl, n-propylcyclopentadienylzirconium dichloride.

The unimodal polyethylene component can in certain cases be formed ingas phase polymerization.

The unimodal polyethylene component can in certain cases be formed froma polymerization conducted in the presence of chromium based catalysts.

The composition can in certain cases have a high molecular weightpolyethylene component having a high weight average molecular weight(MW_(HMW)) and a low molecular weight polyethylene component having alow weight average molecular weight (MW_(LMW)) wherein the spread isless than 95% of the spread of the bimodal component.

One or more specific embodiments of the compositions described hereininclude a bimodal polyethylene. In certain embodiments, a bimodalpolyethylene for the composition may be prepared as described in U.S.Pat. Nos. 6,605,675 or 6,608,149, both of which are incorporated byreference, particularly the aspects that disclose and teach thepreparation of bimodal polyethylene.

Polymerization Processes

The polymerization process used to form any of the polymers describedherein, e.g., either of the polyethylene components used to make theblends, may be carried out using any suitable process, for example, highpressure, solution, slurry or gas phase. The blends may in certainembodiments be “reactor blends” that involve the use of two or moresequential, e.g., cascading, reactors; or the blends may in certainembodiments be physical blends; or in certain embodiments the blends maybe made using a single reactor using two or more catalysts (same ordifferent), but preferably the blends are formed in a single gas-phasereactor using a bimetallic catalyst system.

Certain polyethylenes can be made using a gas phase polymerizationprocess, e.g., utilizing a fluidized bed reactor. This type reactor andmeans for operating the reactor are well known and completely describedin, for example, U.S. Pat. Nos. 3,709,853; 4,003,712; 4,011,382;4,302,566; 4,543,399; 4,882,400; 5,352,749; 5,541,270; EP-A-0 802 202and Belgian Patent No. 839,380. These patents disclose gas phasepolymerization processes wherein the polymerization medium is eithermechanically agitated or fluidized by the continuous flow of the gaseousmonomer and diluent.

In one embodiment, any of the polyethylene components may be polymerizedusing a continuous gas phase process such as a fluid bed process, forexample. A fluid bed reactor may comprise a reaction zone and aso-called velocity reduction zone. The reaction zone may comprise a bedof growing polymer particles, formed polymer particles and a minoramount of catalyst particles fluidized by the continuous flow of thegaseous monomer and diluent to remove heat of polymerization through thereaction zone. Optionally, some of the re-circulated gases may be cooledand compressed to form liquids that increase the heat removal capacityof the circulating gas stream when readmitted to the reaction zone. Asuitable rate of gas flow may be readily determined by simpleexperiment. Make up of gaseous monomer to the circulating gas stream isat a rate equal to the rate at which particulate polymer product andmonomer associated therewith is withdrawn from the reactor and thecomposition of the gas passing through the reactor is adjusted tomaintain an essentially steady state gaseous composition within thereaction zone. The gas leaving the reaction zone is passed to thevelocity reduction zone where entrained particles are removed. Finerentrained particles and dust may be removed in a cyclone and/or finefilter. The gas is passed through a heat exchanger wherein the heat ofpolymerization is removed, compressed in a compressor and then returnedto the reaction zone.

The reactor temperature of the fluid bed process herein preferablyranges from 30° C. or 40° C. or 50° C. to 90° C. or 100° C. or 110° C.or 120° C. or 150° C. In general, the reactor temperature is operated atthe highest temperature that is feasible taking into account thesintering temperature of the polymer product within the reactor.Regardless of the process used to make the polyolefins of the invention,the polymerization temperature, or reaction temperature should be belowthe melting or “sintering” temperature of the polymer to be formed.Thus, the upper temperature limit in one embodiment is the meltingtemperature of the polyolefin produced in the reactor.

A slurry polymerization process can also be used. A slurrypolymerization process generally uses pressures in the range of from 1to 50 atmospheres and even greater and temperatures in the range of 0°C. to 120° C., and more particularly from 30° C. to 100° C. In a slurrypolymerization, a suspension of solid, particulate polymer is formed ina liquid polymerization diluent medium to which ethylene and comonomersand often hydrogen along with catalyst are added. The suspensionincluding diluent is intermittently or continuously removed from thereactor where the volatile components are separated from the polymer andrecycled, optionally after a distillation, to the reactor. The liquiddiluent employed in the polymerization medium is typically an alkanehaving from 3 to 7 carbon atoms, a branched alkane in one embodiment.The medium employed should be liquid under the conditions ofpolymerization and relatively inert. When a propane medium is used theprocess must be operated above the reaction diluent critical temperatureand pressure. In one embodiment, a hexane, isopentane or isobutanemedium is employed.

Also useful is particle form polymerization, a process where thetemperature is kept below the temperature at which the polymer goes intosolution. Other slurry processes include those employing a loop reactorand those utilizing a plurality of stirred reactors in series, parallel,or combinations thereof. Non-limiting examples of slurry processesinclude continuous loop or stirred tank processes. Also, other examplesof slurry processes are described in U.S. Pat. No. 4,613,484 and 2Metallocene-Based Polyolefins 322-332 (2000).

These processes can be used for the production of homopolymers ofolefins, particularly ethylene, and/or copolymers, terpolymers, and thelike, of olefins, particularly ethylene, and at least one or more otherolefin(s). Preferably the olefins are α-olefins. The olefins, forexample, may contain from 2 to 16 carbon atoms in one embodiment; and inanother embodiment, ethylene and a comonomer comprising from 3 to 12carbon atoms in another embodiment; and ethylene and a comonomercomprising from 4 to 10 carbon atoms in yet another embodiment; andethylene and a comonomer comprising from 4 to 8 carbon atoms in yetanother embodiment. Particularly preferred are polyethylenes. Suchpolyethylenes are preferably homopolymers of ethylene and interpolymersof ethylene and at least one α-olefin wherein the ethylene content is atleast about 50% by weight of the total monomers involved. Exemplaryolefins that may be utilized herein are ethylene, propylene, 1-butene,1-pentene, 1-hexene, 1-heptene, 1-octene, 4-methylpent-1-ene, 1-decene,1-dodecene, 1-hexadecene and the like. Also utilizable herein arepolyenes such as 1,3-hexadiene, 1,4-hexadiene, cyclopentadiene,dicyclopentadiene, 4-vinylcyclohex-1-ene, 1,5-cyclooctadiene,5-vinylidene-2-norbornene and 5-vinyl-2-norbornene, and olefins formedin situ in the polymerization medium. When olefins are formed in situ inthe polymerization medium, the formation of polyolefins containing longchain branching may occur.

In the production of polyethylene or polypropylene, comonomers may bepresent in the polymerization reactor. When present, the comonomer maybe present at any level with the ethylene or propylene monomer that willachieve the desired weight percent incorporation of the comonomer intothe finished resin. In one embodiment of polyethylene production, thecomonomer is present with ethylene in a mole ratio range of from 0.0001(comonomer:ethylene) to 50, and from 0.0001 to 5 in another embodiment,and from 0.0005 to 1.0 in yet another embodiment, and from 0.001 to 0.5in yet another embodiment. Expressed in absolute terms, in makingpolyethylene, the amount of ethylene present in the polymerizationreactor may range to up to 1000 atmospheres pressure in one embodiment,and up to 500 atmospheres pressure in another embodiment, and up to 200atmospheres pressure in yet another embodiment, and up to 100atmospheres in yet another embodiment, and up to 50 atmospheres in yetanother embodiment.

Hydrogen gas is often used in olefin polymerization to control the finalproperties of the polyolefin, such as described in PolypropyleneHandbook 76-78 (Hanser Publishers, 1996). Using certain catalystsystems, increasing concentrations (partial pressures) of hydrogen canincrease the melt flow rate (MFR) (also referred to herein as melt index(MI)) of the polyolefin generated. The MFR or MI can thus be influencedby the hydrogen concentration. The amount of hydrogen in thepolymerization can be expressed as a mole ratio relative to the totalpolymerizable monomer, for example, ethylene, or a blend of ethylene andhexane or propene. The amount of hydrogen used in the polymerizationprocess of the present invention is an amount necessary to achieve thedesired MFR or MI of the final polyolefin resin. In one embodiment, themole ratio of hydrogen to total monomer (H₂:monomer) is in a range offrom greater than 0.0001 in one embodiment, and from greater than 0.0005in another embodiment, and from greater than 0.001 in yet anotherembodiment, and less than 10 in yet another embodiment, and less than 5in yet another embodiment, and less than 3 in yet another embodiment,and less than 0.10 in yet another embodiment, wherein a desirable rangemay comprise any combination of any upper mole ratio limit with anylower mole ratio limit described herein. Expressed another way, theamount of hydrogen in the reactor at any time may range to up to 5000ppm, and up to 4000 ppm in another embodiment, and up to 3000 ppm in yetanother embodiment, and between 50 ppm and 5000 ppm in yet anotherembodiment, and between 500 ppm and 2000 ppm in another embodiment.

Further, it is common to use a staged reactor employing two or morereactors in series, wherein one reactor may produce, for example, a highmolecular weight component and another reactor may produce a lowmolecular weight component. In one embodiment of the invention, thepolyolefin is produced using a staged gas phase reactor. Such commercialpolymerization systems are described in, for example, 2Metallocene-Based Polyolefins 366-378 (John Scheirs & W. Kaminsky, eds.John Wiley & Sons, Ltd. 2000); U.S. Pat. No. 5,665,818, U.S. Pat. No.5,677,375; U.S. Pat. No. 6,472,484; EP 0 517 868 and EP-A-0 794 200.

The one or more reactor pressures in a gas phase process (either singlestage or two or more stages) may vary from 100 psig (690 kPa) to 500psig (3448 kPa), and in the range of from 200 psig (1379 kPa) to 400psig (2759 kPa) in another embodiment, and in the range of from 250 psig(1724 kPa) to 350 psig (2414 kPa) in yet another embodiment.

The gas phase reactor employing the catalyst system described herein iscapable of producing from 500 lbs of polymer per hour (227 Kg/hr) to200,000 lbs/hr (90,900 Kg/hr), and greater than 1000 lbs/hr (455 Kg/hr)in another embodiment, and greater than 10,000 lbs/hr (4540 Kg/hr) inyet another embodiment, and greater than 25,000 lbs/hr (11,300 Kg/hr) inyet another embodiment, and greater than 35,000 lbs/hr (15,900 Kg/hr) inyet another embodiment, and greater than 50,000 lbs/hr (22,700 Kg/hr) inyet another embodiment, and from 65,000 lbs/hr (29,000 Kg/hr) to 100,000lbs/hr (45,500 Kg/hr) in yet another embodiment.

A slurry or gas phase process can be operated in the presence of a bulkyligand metallocene-type catalyst system and in the absence of, oressentially free of, any scavengers, such as triethylaluminum,trimethylaluminum, tri-isobutylaluminum and tri-n-hexylaluminum anddiethyl aluminum chloride, dibutyl zinc and the like. By “essentiallyfree”, it is meant that these compounds are not deliberately added tothe reactor or any reactor components, and if present, are present toless than 1 ppm in the reactor.

One or all of the catalysts can be combined with up to 10 wt % of ametal-fatty acid compound, such as, for example, an aluminum stearate,based upon the weight of the catalyst system (or its components), suchas disclosed in U.S. Pat. Nos. 6,300,436 and 5,283,278. Other suitablemetals include other Group 2 and Group 5-13 metals. In an alternateembodiment, a solution of the metal-fatty acid compound is fed into thereactor. In yet another embodiment, the metal-fatty acid compound ismixed with the catalyst and fed into the reactor separately. Theseagents may be mixed with the catalyst or may be fed into the reactor ina solution or a slurry with or without the catalyst system or itscomponents.

Supported catalyst(s) can be combined with the activators and arecombined, such as by tumbling and other suitable means, with up to 2.5wt % (by weight of the catalyst composition) of an antistatic agent,such as an ethoxylated or methoxylated amine, an example of which isKemamine AS-990 (ICI Specialties, Bloomington Del.).

Catalysts

All polymerization catalysts including conventional transition metalcatalysts and metallocene catalysts or combinations thereof, aresuitable for use in embodiments of the processes of the presentinvention. Also contemplated are catalysts such as AlCl3, cobalt, iron,palladium, chromium/chromium oxide or “Phillips” catalysts. Thefollowing is a non-limiting discussion of the various polymerizationcatalysts useful in the invention.

General Definitions relating to Catalysts

As used herein, the phrase “catalyst system” includes at least one“catalyst component” and at least one “activator”, alternately at leastone cocatalyst. The catalyst system may also include other components,such as supports, and is not limited to the catalyst component and/oractivator alone or in combination. The catalyst system may include anynumber of catalyst components in any combination as described herein, aswell as any activator in any combination as described herein.

As used herein, the phrase “catalyst compound” includes any compoundthat, once appropriately activated, is capable of catalyzing thepolymerization or oligomerization of olefins, the catalyst compoundcomprising at least one Group 3 to Group 12 atom, and optionally atleast one leaving group bound thereto.

As used herein, the phrase “leaving group” refers to one or morechemical moieties bound to the metal center of the catalyst componentthat can be abstracted from the catalyst component by an activator, thusproducing the species active towards olefin polymerization oroligomerization. The activator is described further below.

As used herein, in reference to Periodic Table “Groups” of Elements, the“new” numbering scheme for the Periodic Table Groups are used as in theCRC Handbook of Chemistry and Physics (David R. Lide ed., CRC Press81^(st) ed. 2000).

As used herein, the term “substituted” means that the group followingthat term possesses at least one moiety in place of one or morehydrogens in any position, the moieties selected from such groups ashalogen radicals (for example, Cl, F, Br), hydroxyl groups, carbonylgroups, carboxyl groups, amine groups, phosphine groups, alkoxy groups,phenyl groups, naphthyl groups, C₁ to C₁₀ alkyl groups, C₂ to C₁₀alkenyl groups, and combinations thereof. Examples of substituted alkylsand aryls includes, but are not limited to, acyl radicals, alkylaminoradicals, alkoxy radicals, aryloxy radicals, alkylthio radicals,dialkylamino radicals, alkoxycarbonyl radicals, aryloxycarbonylradicals, carbomoyl radicals, alkyl- and dialkyl-carbamoyl radicals,acyloxy radicals, acylamino radicals, arylamino radicals, andcombinations thereof.

Metallocene Catalyst Component

The catalyst system useful in embodiments of the present inventioninclude at least one metallocene catalyst component as described herein.Metallocene catalyst compounds are generally described throughout in,for example, 1 & 2 Metallocene-Based Polyolefins (John Scheirs & W.Kaminsky eds., John Wiley & Sons, Ltd. 2000); G. G. Hlatky in 181Coordination Chem. Rev. 243-296 (1999) and in particular, for use in thesynthesis of polyethylene in 1 Metallocene-Based Polyolefins 261-377(2000). The metallocene catalyst compounds as described herein include“half sandwich” and “full sandwich”compounds having one or more Cpligands (cyclopentadienyl and ligands isolobal to cyclopentadienyl)bound to at least one Group 3 to Group 12 metal atom, and one or moreleaving group(s) bound to the at least one metal atom. Hereinafter,these compounds will be referred to as “metallocenes” or “metallocenecatalyst components”. The metallocene catalyst component is supported ona support material in an embodiment, and may be supported with orwithout another catalyst component.

The Cp ligands are one or more rings or ring system(s), at least aportion of which includes π-bonded systems, such as cycloalkadienylligands and heterocyclic analogues. The ring(s) or ring system(s)typically comprise atoms selected from the group consisting of Groups 13to 16 atoms, or the atoms that make up the Cp ligands are selected fromthe group consisting of carbon, nitrogen, oxygen, silicon, sulfur,phosphorous, germanium, boron and aluminum and combinations thereof,wherein carbon makes up at least 50% of the ring members. Or the Cpligand(s) are selected from the group consisting of substituted andunsubstituted cyclopentadienyl ligands and ligands isolobal tocyclopentadienyl, non-limiting examples of which includecyclopentadienyl, indenyl, fluorenyl and other structures. Furthernon-limiting examples of such ligands include cyclopentadienyl,cyclopentaphenanthreneyl, indenyl, benzindenyl, fluorenyl,octahydrofluorenyl, cyclooctatetraenyl, cyclopentacyclododecene,phenanthrindenyl, 3,4-benzofluorenyl, 9-phenylfluorenyl,8-H-cyclopent[a]acenaphthylenyl, 7H-dibenzofluorenyl, indeno[1,2-9]anthrene, thiophenoindenyl, thiophenofluorenyl, hydrogenatedversions thereof (e.g., 4,5,6,7-tetrahydroindenyl, or “H₄Ind”),substituted versions thereof, and heterocyclic versions thereof.

Group 15-containing Catalyst Component

One aspect of the present invention includes the use of so called “Group15-containing” catalyst components as described herein as a desirablecatalyst component, either alone or for use with a metallocene or otherolefin polymerization catalyst component. Generally, “Group15-containing catalyst components”, as referred to herein, include Group3 to Group 12 metal complexes, wherein the metal is 2 to 8 coordinate,the coordinating moiety or moieties including at least two Group 15atoms, and up to four Group 15 atoms. In one embodiment, the Group15-containing catalyst component is a complex of a Group 4 metal andfrom one to four ligands such that the Group 4 metal is at least 2coordinate, the coordinating moiety or moieties including at least twonitrogens. Representative Group 15-containing compounds are disclosedin, for example, WO 99/01460; EP A1 0 893 454; U.S. Pat. No. 5,318,935;U.S. Pat. No. 5,889,128; U.S. Pat. No. 6,333,389 B2 and U.S. Pat. No.6,271,325 B1.

In one embodiment, the Group 15-containing catalyst components useful inembodiments of the present invention include Group 4 imino-phenolcomplexes, Group 4 bis(amide) complexes, and Group 4 pyridyl-amidecomplexes that are active towards olefin polymerization to any extent.

Activator

As used herein, the term “activator” is defined to be any compound orcombination of compounds, supported or unsupported, which can activate asingle-site catalyst compound (e.g., metallocenes, Group 15-containingcatalysts), such as by creating a cationic species from the catalystcomponent. Typically, this involves the abstraction of at least oneleaving group (X group in the formulas/structures above) from the metalcenter of the catalyst component. The catalyst components of embodimentsof the present invention are thus activated towards olefinpolymerization using such activators. Embodiments of such activatorsinclude Lewis acids such as cyclic or oligomericpoly(hydrocarbylaluminum oxides) and so called non-coordinatingactivators (“NCA”) (alternately, “ionizing activators” or“stoichiometric activators”), or any other compound that can convert aneutral metallocene catalyst component to a metallocene cation that isactive with respect to olefin polymerization.

It is within the scope of this invention to use Lewis acids such asalumoxane (e.g., “MAO”), modified alumoxane (e.g., “TIBAO”), andalkylaluminum compounds as activators, and/or ionizing activators(neutral or ionic) such as tri (n-butyl)ammoniumtetrakis(pentafluorophenyl)boron and/or a trisperfluorophenyl boronmetalloid precursors to activate metallocenes described herein. MAO andother aluminum-based activators are well known in the art. Ionizingactivators are well known in the art and are described by, for example,Eugene You-Xian Chen & Tobin J. Marks, Cocatalysts for Metal-CatalyzedOlefin Polymerization: Activators, Activation Processes, andStructure-Activity Relationships 100(4) Chemical Reviews 1391-1434(2000). The activators may be associated with or bound to a support,either in association with the catalyst component (e.g., metallocene) orseparate from the catalyst component, such as described by Gregory G.Hlatky, Heterogeneous Single-Site Catalysts for Olefin Polymerization100(4) Chemical Reviews 1347-1374 (2000).

Ziegler-Natta Catalyst Component

The catalyst composition may comprise a catalyst component, which is (orincludes) a non-metallocene compound. In an embodiment, the catalystcomponent comprises a Ziegler-Natta catalyst compound, such as disclosedin Ziegler Catalysts 363-386 (G. Fink, R. Mulhaupt and H. H.Brintzinger, eds., Springer-Verlag 1995); or in EP 103 120; EP 102 503;EP 0 231 102; EP 0 703 246; RE 33,683; U.S. Pat. No. 4,302,565; U.S.Pat. No. 5,518,973; U.S. Pat. No. 5,525,678; U.S. Pat. No. 5,288,933;U.S. Pat. No. 5,290,745; U.S. Pat. No. 5,093,415 and U.S. Pat. No.6,562,905. Examples of such catalysts include those comprising Group 4,5 or 6 transition metal oxides, alkoxides and halides, or oxides,alkoxides and halide compounds of titanium, zirconium or vanadium;optionally in combination with a magnesium compound, internal and/orexternal electron donors (alcohols, ethers, siloxanes, etc.), aluminumor boron alkyl and alkyl halides, and inorganic oxide supports.

Conventional-type transition metal catalysts are those traditionalZiegler-Natta catalysts that are well known in the art. Examples ofconventional-type transition metal catalysts are discussed in U.S. Pat.Nos. 4,115,639, 4,077,904, 4,482,687, 4,564,605, 4,721,763, 4,879,359and 4,960,741. The conventional-type transition metal catalyst compoundsthat may be used in the present invention include transition metalcompounds from Groups 3 to 17, or Groups 4 to 12, or Groups 4 to 6 ofthe Periodic Table of Elements.

These conventional-type transition metal catalysts may be represented bythe formula: MR_(x), where M is a metal from Groups 3 to 17, or a metalfrom Groups 4 to 6, or a metal from Group 4, or titanium; R is a halogenor a hydrocarbyloxy group; and x is the valence of the metal M. Examplesof R include alkoxy, phenoxy, bromide, chloride and fluoride. Examplesof conventional-type transition metal catalysts where M is titaniuminclude TiCl₄, TiBr₄, Ti(OC₂H₅)₃Cl, Ti(OC₂H₅)Cl₃, Ti(OC₄H₉)₃Cl,Ti(OC₃H₇)₂Cl₂, Ti(OC₂H₅)₂Br₂, TiCl₃.1/3AlCl₃ and Ti(OC₁₂H₂₅)Cl₃.

Conventional-type transition metal catalyst compounds based onmagnesium/titanium electron-donor complexes that are useful inembodiments of the invention are described in, for example, U.S. Pat.Nos. 4,302,565 and 4,302,566. Catalysts derived from Mg/Ti/Cl/THF arealso contemplated, which are well known to those of ordinary skill inthe art. One example of the general method of preparation of such acatalyst includes the following: dissolve TiCl₄ in THF, reduce thecompound to TiCl₃ using Mg, add MgCl₂, and remove the solvent.

Conventional-type cocatalyst compounds for the above conventional-typetransition metal catalyst compounds may be represented by the formulaM³M⁴ _(v)X² _(c)R³ _(b-c), wherein M³ is a metal from Group 1 to 3 and12 to 13 of the Periodic Table of Elements; M⁴ is a metal of Group 1 ofthe Periodic Table of Elements; v is a number from 0 to 1; each X² isany halogen; c is a number from 0 to 3; each R³ is a monovalenthydrocarbon radical or hydrogen; b is a number from 1 to 4; and whereinb minus c is at least 1. Other conventional-type organometalliccocatalyst compounds for the above conventional-type transition metalcatalysts have the formula M³R³ _(k), where M³ is a Group IA, IIA, IIBor IIIA metal, such as lithium, sodium, beryllium, barium, boron,aluminum, zinc, cadmium, and gallium; k equals 1, 2 or 3 depending uponthe valency of M³ which valency in turn normally depends upon theparticular Group to which M³ belongs; and each R³ may be any monovalentradical that include hydrocarbon radicals and hydrocarbon radicalscontaining a Group 13 to 16 element like fluoride, aluminum or oxygen ora combination thereof.

EXAMPLES Example 1

This example describes preparation of a 50:50 (wt %) blend (Sample 3) oftwo different polyethylene resins, specifically, a bimodal polyethyleneresin (Sample 1) and a unimodal polyethylene resin (Sample 2). TheSample 1 resin was prepared in a single gas phase reactor from a mixedcatalyst system, wherein the two catalysts were 2,4,6 trimethylephenylzirconium dibenzyl (for generating the higher molecular weight componentof the bimodal polyethylene composition) and bis(n-propylcyclopentadienyl) zirconium dichloride (for generating the lowermolecular weight component). The Sample 2 resin was DGDP-6097, a singlegas-phase unimodal high density polyethylene product from Chrome basedcatalyst and Dow commercial HDPE film product. Granules of the Sample 1resin were mixed and compounded with additives, namely Irganox® 1076(1,000 ppm); Irgafos® 168 (1,500 ppm); and CaSt (750 ppm) on a Prodexsingle screw extruder with two mixing heads. The compounded Sample 1resin was then dry blended with the unimodal resin (Sample 2), to formblended Sample 3. Resin properties and Size Exclusion Chromotography(SEC) data of each Sample are shown in Table 1. Note the spread ofSample 3, the blend composition, has been reduced to 37.9 as compared tothe spread of 65.3 for Sample 1, a bimodal polyethylene.

TABLE 1 Sample: 1 2 3 MI (I₂), 0.067 0.081 0.078 g/10 min. FI(I₂₁), 7.610.67 8.76 g/10 min. MFR (I₂₁/I₂) 115 132.5 113 Density (g/cc) 0.95420.9491 0.9521 Exp. Mn: 5,626 13,749 9,846 Exp. Mw: 288,125 277,386279,037 Exp. Mw/Mn: 51.21 20.18 28.34 Calc. Mn: 5,450 8,397 Calc. Mw:287,954 278,789 Calc. Mw/Mn: 52.83 33.20 LMW Mn: 2,592 3,714 LMW Mw:8,111 12,375 LMW Mw/Mn: 3.13 3.33 LMW Wt %: 46.34% 41.72% HMW Mn:115,024 86,131 HMW Mw: 529,640 469,503 HMW Mw/Mn: 4.60 5.45 HMW Wt %:53.66% 58.28% Spread 65.3 NA 37.9 (HMW MW/ LMW MW)

Samples 1 and 3 were formed into films. They were both film-extruded onan Alpine film extrusion line, which was equipped with a 50 mm, 18:1 L/Dscrew, 100 mm annular die (1 mm die gap). The temperature profile(degrees F) was set at 390/400/400/400/410/410/410/410 for zones1/2/3/4/5/6/7/8. Zones 1 and 2 are for screws. Zones 3, 4 and 5 are foradapter block. Zones 6, 7 and 8 are for die. Blow-up ratio (diameter ofblown bubble divided by die diameter) was maintained at 4.0 throughoutthe runs. The take-up speed was 92 fpm and 184 fpm respectively, for 1.0mil and 0.5 mil films. Cooling air flow rate was adjusted to maintainthe frost line height ratio at 9.0. The frost line height ratio is aratio between the height of frost line and the die diameter. At aconstant output rate, the extrusion head pressure decreased or remainedthe same depending on the slight changes in flow indices of eachcomposition. Table 2 summarizes the film extrusion conditions.

TABLE 2 Die set temp. (° F.) 410 Screw RPM 93 Screw amps 62 Headpressure (psi) 8,500 Rate (lb/hr) 95 FAR (film appearance rate) +40 BUR(blow-up ratio) 4 FHR* (Frost-line Height/Die Diameter) 9

The Sample 1 film made using the procedure described above had hazylines dispersed all over the film surface. The bubble became unstable,moving up and down, as the line speed reached 170 fpm. Collecting even0.5 mil film at a line speed of 170 fpm was difficult. The Maximum LineSpeed where a stable bubble can be maintained was 170 fpm.

The Sample 3 film (made from the 50:50 blend) showed substantialimprovement. Soon after the transition from sample 1 to sample 3, thehazy lines disappeared and a nice homogeneous film texture was observed.The bubble became much more stable. A 0.5 mil film was collectedeffortlessly at 170 fpm due to a very stable bubble. The line speed wasthen increased to 220 fpm from which a 0.3-0.35 mil film sample wascollected, and then increased further to 240 fpm. The Maximum Line Speedwas 240 fpm for the composition used to form Sample 3.

Example 2

This example describes preparation of additional blends that containdifferent proportions of bimodal and unimodal polyethylene resins. Thisexample also discusses films made from those blends; and the testing ofthose films. The bimodal polyethylene (Sample 4) was made using a mixedcatalyst. Specifically, in a 5.6 molar ratio, the mixed catalyst was acombination of bis(2-(pentamethyl-phenylamido)ethyl)amine zirconiumdibenzyl (for the high molecular weight component and bis(n-propylcyclopentadienyl) zirconium dichloride (for the lower molecular weightcomponent). The reactor conditions were 85° C., 0.0035 H₂/C₂ with a0.0070 C₆/C₂ ratio.

The Sample 4 resin had been compounded with the following additives:Irganox® 1076 (1,000 ppm); Irgafos® 168 (1,500 ppm); and CaSt (1,500ppm). Sample 4 was then blended with different amounts (16.3 wt %, 33.4wt %, and 50 wt %) of a unimodal resin, namely, DGDA-5120 (Sample 5), aDow commercial sheet product, to form blend Samples 6, 7, and 8. Table 2describes resin properties and SEC data of the various Samples. All theSamples 6, 7 and 8 exhibited lower spread than the Sample 4, a bimodalpolyethylene.

TABLE 3 Sample: 4 5 6 7 8 MI (I2), g/10 min. 0.059 0.098 0.053 0.0580.056 FI(I21), g/10 min. 7.5 12.7 7.02 7.69 8.31 MFR (I21/I2) 127.6 129131.4 133.1 147.3 Density (g/cc) 0.9505 0.9508 0.9507 0.9505 0.9506 Exp.Mn: 4,351 17,540 4,659 4,961 5,565 Exp. Mw: 324,588 180.173 291,588255,741 226,135 Exp. Mw/Mn: 74.60 10.27 62.59 51.55 40.64 Calc. Mn:4,311 4,712 4,938 5,319 Calc. Mw: 322,732 287,103 253,428 223,343 Calc.Mw/Mn: 74.86 60.93 51.32 41.99 LMW Mn: 2,024 2,149 2,192 2,137 LMW Mw:6,998 8,350 9,059 8,971 LMW Mw/Mn: 3.46 3.89 4.13 4.20 LMW Wt %: 46.04%44.44% 42.98% 38.19% HMW Mn: 121,177 101,852 88,755 66,770 HMW Mw:592,146 510,045 437,612 355,815 HMW Mw/Mn: 4.89 5.01 4.93 5.33 HMW Wt %:53.96% 55.56% 57.02% 61.81% Spread 84.6 NA 61.08 48.3 39.66 (HMW MW/LMWMW)

Example 3

This example describes films made from different polymer compositions.Various samples described in Example 2 were film-extruded at a rate of100 pounds per hour using the Alpine film extrusion line and proceduredescribed above in Example 1. Specifically, films were prepared usingSamples 4, 6, 7 and 8. All the compositions, including Sample 4 (neatresin), were melt compounded.

A film made using Sample 4 exhibited poor film texture with prevalenthazy lines on the film surface. However, no gel could be seen in thefilm sample. The bubble was not stable at a 1.0 mil condition (89 fpm)and showed side-to-side oscillation. As the line speed was increased to175 fpm, the bubble became very unstable, displaying up-and-downmovement. Obtaining a 0.5 mil film was difficult. Accordingly, it wasdetermined that the Maximum Line Speed was less than 175 fpm.

Some improvement was observed for film made from Sample 6 (16.3 wt %blend). The film had good texture and bubble stability, and 0.5 mil filmwas easily collected. However, the Maximum Line Speed was onlyapproximately 185 fpm.

Marked improvement was seen for film made from Sample 7 (33.4 wt %blend), which had better film texture. The Maximum Line Speed wasdetermined to be 200 fpm.

The best results were obtained with Sample 8 (50 wt % blend) from whicha 0.5 mil film was made, having excellent appearance quality. Moreover,a dramatically improved Maximum Line Speed was greater than 220 fpm.

Unlike those samples that were melt compounded, a dry-blendedcomposition (Sample 9) was prepared, made from the same components andamounts as Sample 3. This dry blended product was prepared to determinethe existence of any possible effects during melt compounding, such ascross-linking on the improvement in bubble stability and film texture.That tumble mixed 50:50 blend was then fed to a hopper, and a film wasmade. The texture of the resulting film was homogeneous although not asgood as that of the melt blended product (Sample 3). The dry blendedproduct demonstrated a Maximum Line Speed of over 250 fpm. This provedthat regardless of the preparation method, either melt compounded ordry-blended, the blend compositions enhance the bubble stability andthus the Maximum Line Speed.

Both of the bimodal resins (Samples 1 and 4) had resin flow propertiesof 6-9 FI and 100-160 MFR. However, neither of them produced goodquality film or good bubble stability. Based on the two separate blendstudies, the importance of spread control was demonstrated for meetingimportant film product attributes such as good film quality and goodbubble stability.

Example 4

This example describes preparation of additional blends that containdifferent proportions of bimodal and unimodal polyethylene resins. Thebase resin was a bimodal polyethylene (Sample 10), having 10.6 FI and132.5 MFR, made using a dual catalyst that consists of a titanium basedZiegler-Natta catalyst and a metallocene catalyst, bis(n-butyl Cp) Zrdichloride. Sample 10 resin was then physically blended with differentamounts (10 wt %, 20 wt %, and 30 wt %) of a unimodal resin, namely,DGDA-5120, a Dow UCAT commercial sheet product, to form blend Samples11, 12 and 13. The physical blends were compounded on the Prodex line.To maintain the same thermal history, the base resin (Sample 10) wasre-compounded. The different resin compositions were then film extrudedon the Alpine line using the equipment and procedures described inExample 1. Separately, flow properties and SEC of the compoundsincluding the base resin were measured. The spread of the bimodal resinwas reduced by addition of the unimodal resins. However, the overallflow properties and split remained virtually constant for the blendcompounds. Table 4 describes resin properties and SEC data.

TABLE 4 Sample: 10 11 12 13 I₂₁ 10.6 10.3 10.5 9.9 I₃ 0.08 0.074 0.0740.067 MFR (I₂₁/I₂) 132.5 139.1 141.9 147.7 Exp. Mn: 5,988 6,749 6,4677,100 Exp. Mw: 254,405 248,870 198,606 225,606 Exp. Mw/Mn: 42.49 36.8830.71 31.78 Calc. Mn: 5,492 6,086 5,797 6,370 Calc. Mw: 251,863 246,721198,540 222,217 Calc. Mw/Mn: 45.86 40.54 34.25 34.88 LMW Mn: 2,423 2,7422,690 2,771 LMW Mw: 8,976 10,251 10,454 12,102 LMW Mw/Mn: 3.70 3.74 3.894.37 LMW Wt %: 42.38% 43.27% 44.42% 41.32% HMW Mn: 80,187 87,608 75,35774,650 HMW Mw: 430,496 427,072 348,875 370,153 HMW Mw/Mn: 5.37 4.87 4.634.96 HMW Wt %: 57.62% 56.73% 55.58% 58.68% Spread 47.96 41.66 33.3730.58

The film extrusion tests confirmed that the higher amounts of unimodalresin, corresponding to lower overall spread values, provided betterresults than either the unblended bimodal resin or blends containinglower amounts of unimodal resin (or higher spread). The Maximum LineSpeed and spread value for each sample were 170 fpm and 48 for neatresin Sample 10; 180 fpm and 42 for blend Sample 11; 200 fpm and 33 forblend Sample 12; and 270 fpm and 30 for Sample 13. Film homogeneityimproved in correspondence with the reduction in spread; and hazy linespresent in the unblended, neat resin film were less prominent in thehigher spread blend (Sample 11), and absent in the lower spread samples(Samples 12 and 13).

Example 5

This example was similar to Example 4 except a different bimodal baseresin was used for form the film compositions. Specifically, Sample 14had 8.4 FI and 114 MFR. Samples 15, 16 and 17 were blends containing 10%wt, 20% wt and 30% wt, respectively, of unimodal resin DGDA-5120. Asobserved in Example 4, the spread was reduced in proportion to theamount of unimodal that was added. However, the overall flow propertiesand split remained virtually constant for the blend compounds. Table 5describes resin properties and SEC data of the various Samples.

TABLE 5 Sample: 14 15 16 17 I₂₁ 8.42 8.26 9.28 8.4 I₃ 0.074 0.07 0.0770.069 MFR (I₂₁)/I₂) 114 117.8 121 121.5 Exp. Mn: 7,614 7,970 8,284 9,394Exp. Mw: 305,062 290,033 272,048 270,889 Exp. Mw/Mn: 40.07 36.39 32.8428.84 Calc. Mn: 6,513 6,911 7,147 8,182 Calc. Mw: 300,629 285,269266,862 262,851 Calc. Mw/Mn: 46.16 41.28 37.34 32.13 LMW Mn: 2,695 2,7312,890 3,100 LMW Mw: 8,318 8,619 9,312 10,533 LMW Mw/Mn: 3.09 3.16 3.223.40 LMW Wt %: 39.73% 37.54% 38.17% 35.27% HMW Mn: 98,741 86,183 78,85976,484 HMW Mw: 493,342 451,540 425,886 400,340 HMW Mw/Mn: 5.00 5.24 5.405.23 HMW Wt %: 60.27% 62.46% 61.83% 64.73% Spread 59.31 52.38 45.7438.00

All the samples exhibited the same behavior as those in Example 5. TheMaximum Line Speed and spread value for each sample were 190 fpm and 59for neat resin Sample 14; 205 fpm and 52 for Sample 15; 200 fpm and 46for blend Sample 16; and 275 fpm and 38 for Sample 17.

1. A process for producing a film, comprising: forming a film from ablended polyolefin composition at a line speed of at least 170 feet perminute, wherein the blended polyolefin composition comprises: (a) abimodal polyethylene component that includes a high molecular weightpolyethylene component having a high average molecular weight (MWHMW)and a low molecular weight polyethylene component having a low averagemolecular weight (MWLMW), wherein the ratio of the high averagemolecular weight to the low average molecular weight (MWHMW:MWLMW) is 20or more, wherein the high and low molecular weight polyethylenecomponents of the bimodal polyethylene component are formed in a singlereactor, and (b) a unimodal polyethylene component that comprises morethan 15 wt % of the composition to form a blended polyethylenecomposition.
 2. The process of claim 1, further comprising admixing thebimodal polyethylene component with at least one additive.
 3. Theprocess of claim 1, further comprising admixing the bimodal polyethylenecomponent and the unimodal polyethylene component to form the blendedpolyolefin composition.
 4. The process of claim 1, wherein forming afilm comprises at least one of extruding and blow molding.
 5. Theprocess of claim 4, wherein forming a film further comprises feeding theblended polyolefin composition to an extruder.
 6. The process of claim4, wherein forming a film further comprises melting the blendedpolyolefin composition to form a blended polyolefin melt.
 7. The processof claim 1, wherein forming a film further comprises maintaining ablow-up ratio of at least 4.0 during the formation of the film.
 8. Theprocess of claim 1, wherein forming a film further comprises maintaininga frost line height ratio of least 9.0 during the formation of the film.9. The process of claim 1, wherein the blended polyolefin compositionhas a maximum line speed of 185 fpm.
 10. The process of claim 1, whereinthe blended polyolefin composition has a maximum line speed of 220 fpm.11. The process of claim 1, wherein the blended polyolefin compositionhas a maximum line speed of 275 fpm.
 12. A process for producingpolyolefin films, comprising: admixing: (a) a bimodal polyethylenecomponent that includes a high molecular weight polyethylene componenthaving a high average molecular weight (MWHMW) and a low molecularweight polyethylene component having a low average molecular weight(MWLMW), wherein the ratio of the high average molecular weight to thelow average molecular weight (MWHMW:MWLMW) is 20 or more, wherein thehigh and low molecular weight polyethylene components of the bimodalpolyethylene component are formed in a single reactor, and (b) aunimodal polyethylene component that comprises more than 15 wt % of thecomposition to form a blended polyethylene composition; and forming afilm from the blended polyethylene composition; wherein the film isformed at a line speed of at least 170 feet per minute.
 13. The processof claim 12, further comprising admixing the bimodal polyethylenecomponent with at least one additive.
 14. The process of claim 12,further comprising admixing the bimodal polyethylene component and theunimodal polyethylene component to form the blended polyolefincomposition.
 15. The process of claim 12, wherein forming a filmcomprises at least one of extruding and blow molding.
 16. The process ofclaim 15, wherein forming a film further comprises feeding the blendedpolyolefin composition to an extruder.
 17. The process of claim 15,wherein forming a film further comprises melting the blended polyolefincomposition to form a blended polyolefin melt.
 18. The process of claim12, wherein forming a film further comprises maintaining a blow-up ratioof at least 4.0 during the formation of the film.
 19. The process ofclaim 12, wherein forming a film further comprises maintaining a frostline height ratio of at least 9.0 during the formation of the film. 20.The process of claim 12, wherein the blended polyethylene compositionhas a maximum line speed of 185 fpm.
 21. The process of claim 12,wherein the blended polyethylene composition has a maximum line speed of220 fpm.
 22. The process of claim 12, wherein the blended polyethylenecomposition has a maximum line speed of 275 fpm.